TerryE

We've already started some of this feedback on your other thread, so I won't repeat myself here. Correct, large areas of S & W glass will give to U-value losses in the winter and large solar gains Spring - Autumn. You will really need to include your cooling solution for these rooms if you aren't going to cook. As @joe90 suggests having a separate environmental zone external to the main fabric of the house such as a conservatory or atrium might the best of both worlds. If you get the spec of the house correct then you will only need the equivalent of an average 1-2 kW heat input during the winter and UFH on the ground floor is more than enough to provide this. Yes IMO, solar gain can be a net benefit during winter, but localised overheating in the other three months is a pain in the a**e to control.

AnonymousBosch vs HieronymusBosch. Is there some subtle inference here? This one deserves an explanation! ??

@epsilonGreedy I do use a 3kW inline heater, and my current heating algo computes a predicted amount at midnight for the coming 24 hrs based on (1) the forecast average temperate for the following day, and (2) an adjustment based on the average temperature for the last 24 hrs. It will then run the inline heater over night for up to 7 hrs overnight or the calculated amount (which ever is the lesser) to take advantage of E7 tariff. The excess, if any, is only used if the hall temperature falls under a preset (currently 22.3°C). At the moment with the outside temperature bubbling along at around 8-9°C we need about 15kW top up overnight. Looking at my historic logs, this peaked at 40kWh on a few very cold days in Jan but the Jan actuals average was still only 23 kWh and March was 16 kWh / day. We also used a small electric oil-filled radiator in my upstairs office which ran 7 hours @ ~1 kW for a total of maybe 60 days during peak winter. This added heat using E7 cheap rate upstairs rather than adding extra heat to the slab during peak hours. (The 40 kW peaks were before I started doing this). The main difference that the ASHP will make is its CoP of ~3½ when heating water to <35 °C and this will factor down the heating energy accordingly. and it will be cheaper to heat the slab during the day than use the oil-filled radiator overnight. And yes, like Jeremy's, our house does exceed the Passiv spec by a margin. Also remember that pretty much all energy use (excluding bathwater going down the plug hole) ends up as waste heat inside the house, as well as any solar gain, of course. Another advantage of our house is the very long decrement delays of the external fabric, so we only need to be concerned with overall average temperatures, and the predicted bills are largely driven by monthly averaged temperatures. Exceeding this minimum cost was largely by design and by attention to detail during construction; it didn't materially add to the build costs, our heating system is cheap and almost zero maintenance cost. The UFH added less than £2K to the cost of the slab; the UFH manifolds, relays, inline heater, RPi, sensors, etc. less than another £2K. No rads or other heating in the rest of the house; no gas supply or gas appliances ...

As Jack says you can comfortably exceed BRs for little net impact on cost. U-values for walls 0.15, floor and ceiling 0.12, fenestration 0.8 airtightness 1.0 ACH, or better for all. The planners wouldn't allow us to install PV but our total energy bill (electric only) this year has been about £1,400. Our rates are 2× this. Next year after we've installed the ASHP, this will fall to around £800. No gas; no gas boiler service costs; no radiators anywhere, just UFH on the ground floor and house stays between 22-23°C 24×7 year round. So it can be done. We are in our 60s, so everything is design with little or no lifetime maintenance required. Trawl the site; ask Qs; get yourself invited to look around the houses of other members who have gone through this journey, as you will find these face-to-face 1-1s extremely informative.

A bit of a mistake for the very reason that you mention. So you should really make an effort to do this lagging properly and the sooner the easier. As Jeremy says, the SunAmps are amazing for their low heat losses (maybe just over 1kWh /day for two). I have all of my plant for the DHW, CW, UFH including a Harvey water filter and 2×SunAmp PVs in a 700×1400 full height services cupboard off our ground-floor toilet. All of our hot runs are lagged and our DHW manifolds are in a lagged box. The cupboard temp is typically about 2°C warmer than the ground floor rooms. (The MVHR unit is in the store room on the 3rd floor). So it can be done.

It depends on the room sizes etc. We have a 3 floor house with fairly narrow (~3.3m) rooms and use 15mm plasterboard , so the volume of plasterboard is pretty close to that of the 100mm slab. The specific heat capacities of plaster and concrete are pretty much identical. The decrement delay of a single-wall TF with PUR insulation is quite low, but that of a twin-wall TF with cellulosic filler is very high. In our case we also have an external stone skin which also extends the overall DDF. Ours is over a day, and what that means in practice is that we can ignore diurnal temperature variations is our heating calcs; daily average temperatures are easily good enough. Our SE facing principle elevation does act as good external heat store and as Jeremy says, it does heat up and hold this heat especially on these clear sunny mornings that we've been having.

It is well worth making up a second one complete with software install to act as a cold-swap spare -- just in case something does fail in a couple of years: you can swap out the unit and work out went wrong with the old one in slow time.

Unlike mass which has a very precise definition (and nothing to do with heat, BTW) , if you stick an adjective thermal in front of it which means "relating to heat" have "thermal mass" a bit of an oxymoron which is a concept and without any accepted definition and can be overloaded pretty much with whatever message you want. Take the PDF that Ian originally referenced: it was authored by the Concrete Centre and has one dominant message running through it: use lots of concrete in your construction. I've modelled the thermal performance of our house in some detail. A large part of our slab is the load bearing ring and cross beams and actually plays little active roll in stabilising the house temperature; the floor slab itself does. However, the entire plasterboard throughout the fabric of the interior has just as large an effect and in terms of the overall decrement delay performance of the house by far the dominant component is the cellulosic filler used as insulation. This is because this time constant is directly related to the ratio thermal capacity / thermal conductivity, and unlike most wall fabrics which either have very poor thermal capacity or high thermal conductivity, this filler has pretty much the best combination to give good U-value performance coupled with high decrement delay. The last factor in the stability of my house is that I have relatively small window areas and no "acres of south facing glass" so don't have to cope with the solar gain tiger. So both my and Jeremy's houses have extremely low heat loss and high thermal stability, but these use a construction technique not even mentioned in the paper, and the only mention of timber frame construction is in a table on P14 where it is listed as having the worst decrement delay. So the message is: don't use TF construction if you want thermally stable construction. This shows the bias of the authors, and in the case of a Larson strut construction with cellulosic infill this is quite simple a load of bollocks.

@kxi, you might well be right re VAT elligabilty and permissions, so long as you've checked and not assumed.?

One of the sometimes wonderful and sometimes annoying characteristics of this forum is that the posting thread can quickly go off topic -- gold dust interleaved with interesting ramblings. Anything to do with PH and PH certification is off topic. Concentrate on establishing what level of energy efficiency you want and at what price. Conversion vs new build. Establish whether your VAT rating is going to be 0 or 20% -- I suspect that you will probably end up paying VAT at 20% on a conversion. Planning. Your need to establish whether the conversion falls under permitted development rights in which case you need a certificate of lawful development to protect yourself, or whether you will need to go through a full planning application and approval. BReg compliance. You will need to demonstrate that your conversion complies with current BRegs and get the work properly signed off by an approved Build Control Inspector. This may not be trivial for a non-standard conversions. You will almost certainly need a structural engineer to sign-off on the construction. Architect and Proj Mgr overheads -- do you need then or are you going to do the work yourself / use an Architect Technician. Lots of discussions on the forum about the pros and cons here. Thermal performance: if you get the U-value of the walls / ceiling / floor truly under 0.15 and the Air-tightness under 1, with MHVR then you will need minimal heating. Fenestration. You won't achieve an <1 ACH with trickle vents and unsealed windows, but wherever possible stick to good quality stock-size triple-glazed double-sealed windows. There are some Polish suppliers that do very cost-effective units. Reading and researching here and around will pay dividends.

One of the sometimes wonderful and sometimes annoying characteristics of this forum is that the posting thread can quickly go off topic -- gold dust interleaved with interesting ramblings. Anything to do with PH and PH certification is off topic. Concentrate on establishing what level of energy efficiency you want and at what price. Conversion vs new build. Establish whether your VAT rating is going to be 0 or 20% -- I suspect that you will probably end up paying VAT at 20% on a conversion. Planning. Your need to establish whether the conversion falls under permitted development rights in which case you need a certificate of lawful development to protect yourself, or whether you will need to go through a full planning application and approval. BReg compliance. You will need to demonstrate that your conversion complies with current BRegs and get the work properly signed off by an approved Build Control Inspector. This may not be trivial for a non-standard conversions. You will almost certainly need a structural engineer to sign-off on the construction. Architect and Proj Mgr overheads -- do you need then or are you going to do the work yourself / use an Architect Technician. Lots of discussions on the forum about the pros and cons here. Thermal performance: if you get the U-value of the walls / ceiling / floor truly under 0.15 and the Air-tightness under 1, with MHVR then you will need minimal heating. Fenestration. You won't achieve an <1 ACH with trickle vents and unsealed windows, but wherever possible stick to good quality stock-size triple-glazed double-sealed windows. There are some Polish suppliers that do very cost-effective units. Reading and researching here and around will pay dividends.

We just use the HDMI connections into our TV. My Humax, Chromecast and Laptop all have HDMI outputs anyway. The two satellite cables go into the Humax. which is on a shelf below the TV.

They typically work off the street scene, though the rear height can be relevant if you have neighbours near. If your plot does fall away from the road, then setting the house down relative to the road is an important option that you should explore, as well as having gables. More work yes, but you also need to consider that the increased market value of a house having loft rooms that comply with the requirements for bedroom space.

Have you though of upgrading to a Humax DVR? We drive our TV through the Humax. I can't remember the last time that I watched live TV. I don't recall doing it once in the new house. We record and time shift (absolutely essential IMO for the channels with ads) or watch iPlayer / Netflix through the Humax. We also have a Chromecast, but about the only time that I use it is for occasionally casting YouTube, since the Google integration is smoother.

This is misleading as a general observation. Yes, the heating system has to cope with worst case conditions, but the expected running costs are based on appropriately seasonal weighted averages. For example if you are running one of the Mitsubishi Ecodan's with an outlet temp of 35°C (the sort of temp to feed into UFH) then the CoP is just over 4 at an external temp of 7°C falling to around 2.8 at -3°C. How many days a year do we have average temperatures below -3°C?

+1 An expert could do it single handed, albeit a lot slower. This is one to buy in a labourer to help.

If you want to do any major restructuring then the first step is to survey before and after plans so you can look at movement / cut and fill options. Also dig test holes to look at soil profiles. If you have enough topsoil depth then probably the easiest option is to get someone in with a min-digger and blade. But if the soil depth is less than the cut amounts, then the work goes up about 3× because you need to scrape off the topsoil, re-level and then replace a topsoil layer.

We've got living space in our loft as well, with a lot of complaints from neighbours re the ridge height so we went through a lot of similar hassles balancing the build up of the levels to ridge height. Our house works with no complaints, but our ridge height still worked out at 8640, and IIRC this gives us around a 1.6m ridge corridor with head clearance above 1.9m but we also have a rear gable in my son's bedsit and the T head clearance makes the whole space workable. In my previous house we converted a barn extension into a split 1½ storey living area with the other half a kitchen and sleeping area above. The sleeping area was quite spacious (I used it as an office when I still worked), but it was a real PITA only having a ~30cm ridge corridor where I could walk without stooping -- and when we came to sell the property, the estate agents wouldn't classify it as a bedroom because of the head-height. So some points to consider: We had a rise from the road access to the house of ~0.7m. We did a lot of relevelling and removed ~400-500 tonnes of subsoil off site to allow us drop the ground level to road + 0.1m or FFL to road + 0.25m which gave us another 0.45m to play with relative to the street scene profiles. You might consider MMA options to do something similar. Our room heights are 2.4m (ground floor) and 2.3m (1st floor). The 2.3 works fine and doesn't feel limiting. You need to be very careful about ridge height if this is an issue locally. The last thing that you want is for planning enforcement to pick this up and put a stop order on you and force you to do major rework. This is a judgment call but have a look at other enforcement actions and precedent before deciding that an extra 250mm is a cheeky shoe-in. Having a gable in-roof to create a T ridge in the main loft room can significantly increase the effective head-height area. Having interior load bearing walls can allow you to replan your joist layouts and dramatically reduce joist depth. Do a very detailed profile of the roof build-up. In our case we have a passive-class warm roof: I beam ridge, with 300mm rafters and insulation, 25mm service cavity and 15mm pboard on the inside; 18mm sarking, counter battening and battening + slate on the outside -- all × 1.41 in height terms because of the 45% pitch. Add the air breathing ridge capping and this buildup is over 0.5m. If you have (dummy) gable chimneys then consider other options such as having a flattened ridge. The dilemma here is deciding how much to share with the LPA in trying to evaluate options, and this is something that we and your planning consultant will need to evaluate in the local context. We found pre-planning advice extremely useful in getting the LPA support, but other members here can tell nightmare stories.

I really don't think that this is an evidence-based view, and is hardly a good reason for adding £10K or so to your costs as well as digging up a large chunk of your site.

No. Your LPA will have local guidelines, relating to housing density in your locale. In our case in our village it was 7m. And even so these are guidelines, not regulations. The LPA might vary them depending on local conditions, e.g. if your closest point is only single storey; if there is a line of site barrier in the neighbours garden, such as trees with TPO; if the neighbours house is already less than this guideline. Your particular case is best discussed using formal "Pre-planning advice"(PPA), IMO. We found using PPA extremely useful, as our planner gave some very useful advice and some outline recommendations that we followed and he then supported during the application despite neighbours objections, so overall PPA was a useful instrument for us to engage constructively with the LPA. Note however, that some members will no doubt disagree about the risks and benefits of PPA.

We have just mounted a 42" TV on a swivel arm much the same way, but ours uses a vertically orientated mount and comes highly reviewed. As it happened one of the vertical battens (stud in our case) was in a suitable position so we could screw directly into that. It might be worth using a stud finder to locate your studs because if one is suitably positioned, then putting any mounting bolts through this, so the stud acts as the stand-off will save a lot of work.

Ian, health and safety would have a fit looking at your scaffolding, IMO. I thought that you're supposed to have a kick board around the perimeter of the scaffolding to prevent material accidentally falling off the boarding, and you're also supposed to have a safety rail and netting. As this incident shows it can get very windy up there, and the last thing is that you want to happen as the final chapter in your build is getting blown off the scaffolding while finishing off the roof. ?

@Ed Davies you seem to be implying some form of hysteresis in this. Can you cite a basis for this? I can see possible mechanisms for supercriticality, etc, but I wouldn't think that they are critical in the real world. As to EVP vs Dew Point: clearly they aren't the same as one is a pressure and one a temperature, and the only occasion that they are locked is at the triple point, but for a given material such as H2O, they are directly related. But the EVP for a given temperature is the pressure at which the rate of evaporation from a liquid/gas interface is the same as the condensation rate: there is no net evaporation. Coming back to @Triassic's OP and Q, my assertion is that the dew point is largely irrelevant as far as the interior of a well designed insulated wall: so long that there are no construction flaws which lead to internal circulation or mass air flow through the wall profile. For a given temperature profile, the dew point can only be well defined if the AH of the water vapour content can be well defined. For an open celled medium such as wool or cellulosic filler with an interior air tightness membrane, I can't think of any mechanism why the AH should have a systematic gradient as the gas laws would tend to self-level this subject to diffusion rates, and you'd need some form of forcing or pumping mechanism to sustain a gradient. At worst the cavity will be at dew point and since there almost always is a positive thermal gradient through the wall profile, the entire profile should be above the dew point IMO. The only possible interface where this could occur in practice is where there is discontinuity -- e.g. of AH between the room environment and the wall interior at the airtight membrane. And this could lead to surface condensation on such surfaces. But this isn't an interior issue.

Firing on 3½ cylinders is a lot better than on 2½

@Ed Davies Ed, I've spent this last week pondering this one on and off. First, you say "the temperature at which condensation starts on a flat surface of pure water", and I talk about the "equilibrium vapour pressure": there is a shared understanding here, but we are simply using different terminology to describe the same mechanism. Returning to @Triassic's original Q: "what is dew point and why does it matter", we can agree on a definition of the due point, but in my mind the issue is really "when does it matter?" and in my mind what this comes down to is when there is sufficient mass-flow of moist air to create a systemic condensing out of water vapour into its liquid phase on or within the fabric of the build. Direct leakage of water is always going to be a problem and dew point is irrelevant to this. My thesis is that dew point is only relevant when you have mass flow of air, as this is an essential precursor to the delivery of moisture for transfer to the liquid phase at the dew point. So this mass flow scenario and dew point is relevant in the case of MVHR design which is why units include condensate collection and waste removal. It might also become an issue for leaky houses where there are material exhaust flow paths from the interior though the insulation fabric, but for airtight walls the only possible transport is gas diffusion. In the case of closed cell insulation mediums such as PUR/PIR, the very closed cell isolation of insulating gasses is core to their insulation performance: they typically embody a hydrocarbon pentane as the filler gas that has roughly double the R-value of air which is why these materials can claim roughly have the U-value of the same depth of an open cell material such as wool which relies on still air as its main insulating material. However there could be clear flow and circulation paths around slab insulators if poorly fitted and not sealed, but whilst packed materials such as wool and blown cellulosic filler rely on air as the insulator, they are also intrinsically void filling and prevent mass flow: the only transport mechanism is diffusion. In our case we have a Larson strut TF with metal wall ties to an outer stone leaf. In cases of driving rain I could image scenarios where the gap-side surface of the stone skin becomes wet by driving rain through the odd pointing gap, so the air-gap could set to saturated water vapour pressures relative to the temperature of the stone skin, but there are only pathological circumstances when the inner panelling will be at a lower temperature than the stone skin to cause a condensing transport of water across the air-gap. Any surface water on the tenting surface of the frame will cause liquid phase transport of water into the frame structure, but can you think of any circumstances dew point mechanisms (vapour -> liquid transition) will cause material transport of water into the frame? I can't.